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Description

These beetles are recognizable by their bright metallic colours. The head and thorax are usually green, and the elytra (wing covers) are copper. There are five small tufts of white hair on either side of the abdomen. They reach 12 mm long.

The white grubs have brown heads and three sets of legs. They adopt a crescent-shaped position in the soil, and may be up to 32 mm long.

Life cycle

These insects complete their life cycle in one year. The adults emerge in June and July. After mating, the females lay from one to five spherical eggs in moist soil. They can mate several times and produce from 40 to 60 eggs over the summer.

The larvae hatch two weeks later. They feed on plant roots until temperatures drop in the fall. At that point they burrow deeper into the soil, to depths of 10 to 20 cm, to escape the cold. They make their way back toward the surface in the spring and begin feeding again. When they reach maturity, they stop eating and pupate before turning into adults.

Geographic distribution

The species originated in East Asia and was accidentally introduced into the United States, where it was spotted for the first time in 1916 in New Jersey.

It is now found in the west as far as Missouri, with some populations in California. In Canada, it occurs from Ontario to Nova Scotia.

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Habitat

Japanese beetles live in a wide variety of habitats, including gardens, forests and cities, wherever they can find foliage to feed on.

Diet

The larvae feed on the roots of many different plants, grasses in particular.

The adults eat the leaves, flowers and fruit of many different trees, shrubs and grasses (up to 400 species), including grapevines, roses, cherries, soy and willows.

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Interesting facts

Japanese beetles can multiply very quickly. It is best to eliminate them by drowning them in slightly soapy water. This mechanical approach is one of the surest ways to rapidly reduce their populations.

Pheromone traps specially designed for these insects are commercially available, but our flower and vegetable gardens are generally not large enough for these traps to be used efficiently. In fact, they often have the opposite effect, instead attracting these insect pests to one’s yard.

Ecological roles

Japanese beetles are considered crop and garden pests. The larvae damage lawns. The adults, which often feed in swarms, can skeletonize trees and shrubs. They also attack flower buds and fruit.

Mammals (moles, shrews, skunks) and birds feed on the larvae and can control their populations to some extent. Natural predators of the insect (flies and wasps) have been imported from Japan. In fact, we can now see the presence of Istocheta aldrichi, a parasitoid tachinid fly that lays its eggs on Japanese beetles. The fly larva then develops inside the Japanese beetle, resulting in its death. The larva of the fly will then turn into a pupa, always inside the beetle, where it will spend the winter. Adults emerge in spring, around the same time as Japanese beetles. If you see parasitized Japanese beetles, it is important to leave them in the wild so that this predator can continue its life cycle. This is easily recognizable by the white dots (eggs), often on the Japanese beetle's thorax.